Historic Earthquakes

The main earthquake took nine lives and
caused property damage estimated at $6 million.
Damage from a strong aftershock near Brawley
at 05 51 UTC is included in this estimate.

The first shock damaged about 80 percent of
the buildings in Imperial. Many buildings in
the business district were condemned, and older
residences sustained severe damage. Four
people were killed in the collapse of a grocery
store. Damage to a lesser extent occurred at
El Centro and Holtville. Elevated water tanks
at Holtville and Imperial collapsed, and a
water tank at Brawley was damaged.

The
downtown business area at Brawley was damaged
severely by the second shock, and about 25
percent of the houses in the residential area
were damaged. About half of the business
structures had to be condemned. Many breaks in
water mains occurred and water pipes were
broken.

Damage to the structures and canals
of the Imperial Irrigation District in the
United States and Mexico was widespread.
Breaks occurred over almost the entire length
of the Ash Canal, from Holtville to the Mexico
border. The Alamo Canal, the main feeder for
the entire system, had eight major breaks; a
section of the Solfatara Canal in Baja
California was destroyed south of Cocopar. The
earthquake demolished the New River flume, a
427-meter-long timber structure on the West Side
Main Canal south of Mexicali.

Right-lateral
offset occurred along the Imperial fault. The
pattern of offset indicates that the main part
of the offsets occurred along a surface
fracture about 20 to 25 kilometers long, extending from
the epicenter of the main shock southeast,
about 5 kilometers past Cocopar. Rupture of the
northwest section of the fault may have
occurred during a damaging aftershock at 05 51
UTC. Where the surface fracture crosses the
All American Canal east of Calexico, the
largest displacement of 4.5 meters occurred. At one
point on the Solfatara Canal, the slip was as
much as 3.7 meters.

In Baja California, the
Inter-California Railroad track was displaced
at Grape, and about 300 meters of railroad track
settled north of Grape. At Cocopar, the track
shifted 2 meters, and at Meloland, it shifted about
46 centimeters.

Many sand boils were observed near
Gadsden on the Yuma Project in Baja California.
Geysers spouting water several meters high
also were reported. Canals, drainage channels,
flumes, and bridges were damaged near Gadsden.
The main earthquake was felt over much of
southern California, southwest Arizona, and
northern Baja California. About 48 aftershocks
occurred through the end of 1940. Those on May
23 caused more damage at Brawley.

Abridged from
Seismicity of the United States, 1568-1989 (Revised),
by Carl W. Stover and Jerry L. Coffman,
U.S. Geological Survey Professional Paper 1527,
United States Government Printing Office, Washington: 1993.